The structure of organic electroluminescent devices (for example OLEDs—organic light-emitting diodes, or OLECs—organic light-emitting electrochemical cells) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. The emitting materials employed here, besides fluorescent emitters, are increasingly organometallic complexes which exhibit phosphorescence (M. A. Baldo et al., Appl. Phys. Lett. 1999, 75, 4-6). For quantum-mechanical reasons, an up to four-fold increase in energy and power efficiency is possible using organometallic compounds as phosphorescence emitters. In general, there is still a need for improvement, in particular with respect to efficiency, operating voltage and lifetime, both in the case of OLEDs which exhibit singlet emission and also in the case of OLEDs which exhibit triplet emission. This applies, in particular, to OLEDs which emit in the relatively short-wave region, i.e. green and in particular blue.
The properties of organic electroluminescent devices are not determined only by the emitters employed. In particular, the other materials used, such as host and matrix materials, hole-blocking materials, electron-transport materials, hole-transport materials and electron- or exciton-blocking materials, are also of particular importance here. Improvements in these materials can result in significant improvements in electroluminescent devices.
In accordance with the prior art, use is made, inter alia, of ketones (for example in accordance with WO 2004/093207 or WO 2010/006680) or phosphine oxides (for example in accordance with WO 2005/003253) as matrix materials for phosphorescent emitters. Further matrix materials in accordance with the prior art are triazines (for example WO 2008/056746, EP 0906947, EP 0908787, EP 0906948).
For fluorescent OLEDs, use is made in accordance with the prior art of, in particular, condensed aromatic compounds, in particular anthracene derivatives, as host materials, in particular for blue-emitting electroluminescent devices, for example 9,10-bis(2-naphthyl)anthracene (U.S. Pat. No. 5,935,721). WO 03/095445 and CN 1362464 disclose 9,10-bis(1-naphthyl)anthracene derivatives for use in OLEDs. Further anthracene derivatives are disclosed in WO 01/076323, WO 01/021729, WO 2004/013073, WO 2004/018588, WO 2003/087023 or WO 2004/018587. Host materials based on aryl-substituted pyrenes and chrysenes are disclosed in WO 2004/016575. Host materials based on benzanthracene derivatives are disclosed in WO 2008/145239. For high-quality applications, it is desirable to have improved host materials available.
The prior art discloses the use of compounds containing one or more carbazole groups in electronic devices, for example in WO 2005/039246, US 2005/0069729, JP 2004/288381, EP 1205527 or WO 2008/086851.
The prior art furthermore discloses the use of compounds containing one or more indenocarbazole groups in electronic devices, for example in WO 2010/136109 and WO 2011/000455.
The prior art furthermore discloses the use of compounds containing one or more electron-deficient heteroaromatic six-membered rings in electronic devices, for example in WO 2010/015306, WO 2007/063754 and WO 2008/056746.
WO 2009/069442 discloses tricyclic compounds, such as carbazole, dibenzofuran or dibenzothiophene, which are highly substituted by electron-deficient heteroaromatic groups (for example pyridine, pyrimidine or triazine). The tricyclic compounds are not substituted by hole-conducting groups, i.e. electron-rich groups.
JP 2009-21336 discloses substituted carbazoles as matrix materials, where the carbazoles are substituted by an electron-conducting group and by a hole-conducting group. However, the compounds have no face-to-face substitution.
WO 2011/057706 discloses substituted carbazoles as matrix materials, where the carbazoles are substituted by an electron-conducting group and by a hole-conducting group. However, most of the carbazoles disclosed have no face-to-face substitution. In the case of the face-to-face arrangements occasionally disclosed, however, the hole- or electron-conducting group is bonded directly to the tricyclic compound.
However, there is still a need for improvement on use of these materials as in the case of other materials, in particular with respect to the efficiency and the lifetime of the device.